1. Field of the Invention
The present invention relates generally to charging a mobile terminal, and more particularly, to a mobile terminal and a method for receiving wireless charging from another mobile terminal or providing wireless charging to another mobile terminal.
2. Description of the Related Art
Mobile terminals such as mobile phones, Personal Digital Assistants (PDAs), etc., are powered by rechargeable batteries that are charged with electrical energy supplied by a separate charging apparatus. In general, a separate contact terminal is arranged outside of the charging apparatus and the battery, and the charging apparatus and the battery are electrically connected to each other through contact between them.
However, since the contact terminal protrudes outwardly in such a contact-type charging scheme, the contact terminal is easily contaminated by foreign substances, and in such cases, battery charging may not be performed correctly. Further, battery charging may not be performed correctly when the contact terminal is exposed to moisture.
Recently, a wireless charging (i.e., a non-contact charging technology) has been developed and used for electronic devices to address the above-mentioned problems.
Such a wireless charging technology employs wireless power transmission/reception, and corresponds to, for example, a system in which a battery can be automatically charged if the battery is laid on a charging pad, without the need to connect the mobile phone to a separate charging connector. The wireless charging technology is generally used for devices such as a wireless electric toothbrush or a wireless electric shaver. Accordingly, a waterproof function of such devices can be improved, and the portability of such electronic devices can be increased, since there is no need to provide a wired charging apparatus. Technologies related to wireless charging technology are also expected to be significantly developed in the coming age of electric cars.
Wireless charging technology commonly includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and a Radio Frequency (RF)/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
The electromagnetic induction scheme is commonly-used, but it is expected eventually, all electronic products will be charged, at any time and location, without a wire, due to the strength of recent successful experiments for wirelessly transmitting power to a destination dozens of meters away, through the use of microwaves.
A power transmission method through the electromagnetic induction corresponds includes transmitting power between a first coil and a second coil. When a magnet approaches the coil, an induced current is generated. A transmission side generates a magnetic field by using the induced current and a reception side generates energy through an induced current according to changes in the magnetic field. The phenomenon is referred to as magnetic induction, and power transmission methods using magnetic induction transmit energy very efficiently.
Power transmission methods through electromagnetic induction have been commercialized, and are applied to various devices. The electromagnetic induction scheme makes up a majority of the non-contact charging technology corresponding to wireless charging, and this technology was originally applied to products such as electric shavers, electric toothbrushes, etc., using a nickel battery.
Another wireless charging scheme uses resonance. Prof. Soljacic of the Massachusetts Institute of Technology (MIT) announced a system in which electricity is wirelessly transferred using a resonance-based power transmission principle, based on a coupled mode theory that operates even when a device to be charged is separated from a charging device by several meters. This wireless charging system used by an MIT team employs a resonance concept in physics in which, when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork will tend to oscillate at the same frequency. The research team resonated an electromagnetic wave containing electrical energy instead of resonating sounds. The resonated electrical energy is directly transferred only when there is a device having a resonance frequency, and parts of electrical energy that are not used are reabsorbed into an electromagnetic field instead of being spread in the air, so that the electrical energy does not affect surrounding machines or people, in contrast to other electromagnetic waves.
Lastly, there is the RF/microwave radiation scheme. The RF/microwave radiation scheme is a new conceptual power transmission method of converting energy to a microwave favorable to wireless transmission and then transmitting the converted energy. The microwave scheme transmits the power energy instead of a concept of a signal used in the wireless communication technology such as a radio, a wireless phone or the like. While normal communication corresponds to carrying a signal on a carrier signal and then transmitting the carrier signal, the wireless power transmission corresponds to transmitting only the carrier.
A wireless charging system to which the wireless charging technology is applied typically includes a charging stand for supplying power to a terminal. Accordingly, there is a disadvantage in that, in such a system, wireless charging is only possible in locations of charging stands.